The present invention relates generally to a method and apparatus for altering carbon-containing compounds with corona discharge. More specifically, hazardous waste compounds are altered or converted or destroyed to less hazardous compounds or elements with the corona discharge.
Disposal, clean up and/or site remediation of hazardous carbon containing compounds continues to be a challenge, especially for organic compounds that are difficult to oxidize or are xe2x80x9cnon-oxidizablexe2x80x9d. J Hoigne and H Bader, OZONATION OF WATER: SELECTIVITY AND RATE OF OXIDATION OF SOLUTES, Ozone: Science and Engineering, Vol. 1, pp 73-85, 1979 identify the following compounds as xe2x80x9cnot [be] oxidized directly by ozone even during an extended ozonationxe2x80x9d: chloroethylenes including specifically tetrachloroethylene, and trichloroethylene, benzene, aliphatic alcohols, aldehydes, carbonic acids, specifically oxalic acid. Other non-oxidizable compounds include but are not limited to carbon tetrachloride (CCl4), methylisobutylketone (MIBK) also known as hexone, 4-methyl-2-pentanone, perchloroethylene (PCE), and pentachlorophenol (PCP).
Research in this field has been ongoing for many years. In the paper TREATMENT OF LIQUIDS WITH ELECTRIC DISCHARGES, W L Hudson, The American Institute of Chemical Engineers, 1979, various embodiments of xe2x80x9cplasma reactorsxe2x80x9d are shown and discussed. The reactors tend to have the common features of one electrode positioned above or away from the liquid containing the carbon-containing compound to be treated and a second electrode in contact with the liquid containing the carbon-containing compound to be treated. However, Hudson states
The only encouraging success with the treatment of liquids with electric discharges has been in a partial vacuum at or near the vapor pressure of the liquid being treated, more specifically in the pressure range 20 to 70 mm of Hg. If the pressure is less than the vapor pressure of the liquid being treated, the liquid boils, sometime violently. If the pressure increases as a result of gas buildup in the system the discharge might extinguish itself and at best becomes much less efficient.
Hudson does, however, report a test using pulsed discharge at 1 atmosphere pressure. Hudson reports percent reacted of a carbon containing compound as ranging from 7 percent reacted to 92 percent reacted. Compounds reacted were Fe++, and carbon containing compounds reacted of phenol, sewage, and acrylonitrile.
In an article of the Journal of Chemical Society, GLOW DISCHARGE ELECTROLYSIS. PART I. THE ANODIC FORMATION OF HYDROGEN PEROXIDE IN INERT ELECTROLYSIS, R A Davies, A Hickling, pp 3595-3602, 1952, the authors studied the formation of hydrogen peroxide using glow discharge. They observed the influence of varying electrical current, volume of anolyte, surface area, electrode distance, size and shape of electrode, type of gas atmosphere (air, N2, O2, H2, N2O), pressure and type of electrolyte. For type of gas atmosphere, they found no difference in the amount of peroxide production. In a second article in the Journal of Chemical Society, GLOW DISCHARGE ELECTROLYSIS. PART II. THE ANODIC OXIDATION OF FERROUS SULFATE, A Hickling, J K Linacre, pp 711-720, 1954, ferrous sulfate oxidation was studied by varying the same parameters as had been done for hydrogen peroxide formation. Again, it was found that varying the atmosphere from N2 to H2 had no appreciable effect. A minor effect was observed for O2 atmosphere.
In a report, HAZARDOUS WASTE REMEDIAL ACTIONS PROGRAM ANNUAL PROGRESS REPORT, R B Craig, DOE/HWP-102, Martin Marietta Energy Systems, Inc., August 1990, pp 121-125, there is described tests in which air ions, specifically O2xe2x80x94, are used to destroy acrylamide, chlorobenzene, styrene, phenol, benzene, methoxychlor, 2,4-dichlorophenol, chloroform, benzoic acid, and citric acid.
In a paper, THE DEGRADATION OF ORGANIC DYES BY CORONA DISCHARGE, S C Goheen et al., Chemical Oxidation: Technology for the 90""s Conference February 1992, a corona discharge reaction vessel is shown with one electrode suspended above a liquid surface and a second electrode in contact with the liquid. Electricity was applied from 5-15 kV, 10 to 50 xcexcA to degrade organic dyes, specifically Malachite Green, New Coccine, methylene blue, and silicic acid. Air and nitrogen were used and found to influence the amount of electrical current needed, but with no effect on chemical reaction rate, except that oxygen was necessary. There was no reaction with only nitrogen and reaction rate increased with increasing oxygen concentration, thereby concluding, xe2x80x9coxygen is clearly required for the dye to react with species generated by corona dischargexe2x80x9d.
Corona discharges are relatively low-power electrical discharges that can be initiated at or near ambient conditions. The corona is in the gas phase and, when generated with an electrode above a liquid surface and an electrode in contact with the liquid, the corona is also immediately on the liquid surface. It should be noted that corona discharge is not merely another configuration of electrolysis where chemical reactions are accomplished by charge transfer oxidation and reduction. Hickling et al. (cited above) proved that charge transfer is only a minor factor in corona discharge and that the chemical effects are fundamentally different. Most noticeably, many equivalents of chemical reaction can be accomplished for each electron of charge transfer. Each electron accelerating through the electric field collides with many gas molecules creating other charged particles and neutral active species (free radicals and atoms). Depending on the conditions of the discharge active species accounting for between 8 and 180 reactions have been measured for each electron of charge transferred. These can bring about ionization, excitation or dissociation of solvent molecules by collision; in addition to charge transfer reactions observed in a typical electrochemical process.
Corona discharge is most similar to radiolysis or electron beam processes and the concepts and ideas developed in radiation chemistry can be directly applied to this type of corona discharge process as pointed out in by Hickling in his book THE MECHANISM OF CHARGE TRANSFER, Chapter 5, xe2x80x9cElectrochemical Processes in Glow Discharge at the Gas-Solution Interfacexe2x80x9d, pp. 328-373. However, there are some noteworthy differences between the two processes. For example, although the energy per electron in corona discharge is relatively low (xcx9c100 eV) as compared to most ionizing radiation (xcx9c104-107 eV), the dose rate can be extremely high. It was measured by Hickling et al., that for a current of 0.075 A, the number of singly charged gaseous ions reaching the solution surface per minute was 2.8xc3x971019. Assuming an average energy of 100 eV, the dose rate for corona discharge amounts to 2.8xc3x971021 eV minxe2x88x921. This is significantly higher than the dose rate normally used in radiolysis (xcx9c1016-1020 eV ccxe2x88x921 minxe2x88x921). Therefore, the amount of chemical change that can be affected in corona discharge is much greater than that in radiolysis, and high concentrations of substrate can be used. Furthermore, under these conditions, impurities seem to have much less effect (Hickling, ELECTROCHEMICAL PROCESSES IN GLOW DISCHARGE AT THE GAS SOLUTION INTERFACE, pp 329-373, J. of Electroanalytical Chemistry, 1964). Thus, corona discharge is distinct from typical electrochemical processes because it can bring about chemical changes which are similar to those which result from ionizing radiation. Corona discharge is also distinct from radiolysis because the energy input is of the order of an electrochemical process.
The research described above has not resulted in a corona discharge method and apparatus that is capable of cost effectively removing hazardous carbon containing compounds from water, or destroying the hazardous carbon containing compounds in water. Hence, there is still a need for a method and apparatus for altering a carbon containing compound in an aqueous mixture.
The present invention is a method and apparatus for altering a carbon-containing compound in an aqueous mixture. According to a first aspect of the present invention, it has been discovered that for an aqueous mixture having a carbon containing compound with an ozone reaction rate less than the ozone reaction rate of pentachlorophenol, use of corona discharge in a low or non-oxidizing atmosphere increases the rate of destruction of the carbon containing compound compared to corona discharge in an oxidizing atmosphere. For an aqueous mixture containing pentachlorphenol, there was essentially no difference in destruction between atmospheres. According to a second aspect of the present invention, it has been further discovered that an aqueous mixture having a carbon-containing compound in the presence of a catalyst and oxygen resulted in an increased destruction rate of the carbon-containing compound compared to no catalyst.
It is hypothesized that when corona discharge dissociates solvent molecules in a water system it can form free radicals, .H, and .OH. The .OH, hydroxyl, radical is an extremely aggressive oxidizer (oxidation potential 2.80 Volts) and the primary species considered active in advanced oxidation technologies such as UV/O3 and UV/peroxide (and Fenton""s reagent, Fe/peroxide). The energy requirement for PCP destruction by corona discharge was compared with that of UV/O3 process (electricity to power the lamps and generate O3) and was found to substantially match. Further experiments also investigated the destruction of perchloroethylene and carbon tetrachloride with corona discharge. Each was destroyed in laboratory tests to 99+%. These carbon-containing compounds are not considered oxidizable (Perox-pure, a UV/peroxide process cannot successfully treat these carbon containing compounds). Although, the mechanism has not been elaborated, another reaction pathway, besides oxidation by .OH, is believed to play a critical part.
It is an object of the present invention to provide a method and apparatus for destroying a carbon-containing compound in an aqueous mixture with corona discharge.
It is a further object of the present invention to provide a method and apparatus for destroying a carbon containing compound that has an ozone reaction rate less than or equal to pentachlorophenol in a low or non-oxidizing atmosphere.
It is a further object of the present invention to provide a method and apparatus for destroying a carbon-containing compound that has an ozone reaction rate greater than or equal to pentachlorophenol in the presence of a catalyst and oxygen.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of operation, together with further advantages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.